Canola is a genetic variation of rapeseed developed by Canadian plant breeders specifically for its nutritional qualities, particularly its low level of saturated fat. In 1956 the nutritional aspects of rapeseed oil were questioned, especially concerning the high eicosenoic and erucic fatty acid contents.
In the early 1960's, Canadian plant breeders isolated rapeseed plants with low eicosenoic and erucic acid contents. The Health and Welfare Department recommended conversion to the production of low erucic acid varieties of rapeseed. Industry responded with a voluntary agreement to limit erucic acid content to five percent in food products, effective Dec. 1, 1973.
In 1985, the U.S. Food and Drug Administration recognized rapeseed and canola as two different species based on their content and uses. Rapeseed oil is used in industry, while canola oil is used for human consumption. High erucic acid rapeseed (HEAR) oil contains 22-60 percent erucic acid, while low erucic acid rapeseed (LEAR) oil has less than 2 percent erucic acid. Meal with less than 30 μmol/g glucosinolates is from canola. Livestock can safely eat canola meal, but high glucosinolate rapeseed meal should only be fed to cattle because it may cause thyroid problems in monogastric livestock.
Each canola plant produces yellow flowers that, in turn, produce pods, similar in shape to pea pods about ⅕th the size. Within the pods are tiny round seeds that are crushed to obtain canola oil. Each seed contains approximately 40 percent oil. The remainder of the seed is processed into canola meal, which is used as a high protein livestock feed.
Because it is perceived as a “healthy” oil, its use is rising steadily both as a cooking oil and in processed foods. The consumption of canola oil is expected to surpass corn and cottonseed oils, becoming second only to soybean oil. It is low in saturates, high in monounsaturates, and contains a high level of oleic acid. Many people prefer the light color and mild taste of canola oil over olive oil, the other readily available oil high in monounsaturates.
Rapeseed has been grown in India for more than 3000 years and in Europe since the 13th century. The 1950s saw the start of large-scale rapeseed production in Europe. Total world rapeseed/canola production is more than 22.5 million metric tons.
Farmers in Canada began producing canola oil in 1968. Early canola cultivars were known as single zero cultivars because their oil contained 5 percent or less erucic acid, but glucosinolates were high. In 1974, the first licensed double zero cultivars (low erucic acid and low glucosinolates) were grown. Today all canola cultivars are double zero cultivars. Canola has come to mean all rapeseed cultivars that produce oil with less than 2 percent erucic acid and meal with less than 30 μmol/g of glucosinolates.
Canola production uses small grain equipment, limiting the need for large investments in machinery. Planting costs of canola are similar to those for winter wheat. The low investment costs and increasing consumer demand for canola oil make it a potentially good alternative crop.
There are numerous steps in the development of any novel, desirable plant germplasm. Plant breeding begins with the analysis and definition of problems and weaknesses of the current germplasm, the establishment of program goals, and the definition of specific breeding objectives. The next step is selection of germplasm that possess the traits to meet the program goals. The goal is to combine in a single variety an improved combination of desirable traits from the parental germplasm. These important traits may include higher seed yield, resistance to diseases and insects, better stems and roots, tolerance to drought and heat, and better agronomic quality.
Choice of breeding or selection methods depends on the mode of plant reproduction, the heritability of the trait(s) being improved, and the type of cultivar used commercially (e.g., F1 hybrid cultivar, pureline cultivar, etc.). For highly heritable traits, a choice of superior individual plants evaluated at a single location will be effective, whereas for traits with low heritability, selection should be based on mean values obtained from replicated evaluations of families of related plants. Popular selection methods commonly include pedigree selection, modified pedigree selection, mass selection, and recurrent selection.
The complexity of inheritance influences choice of the breeding method. Backcross breeding is used to transfer one or a few favorable genes for a highly heritable trait into a desirable cultivar. This approach has been used extensively for breeding disease-resistant cultivars. Various recurrent selection techniques are used to improve quantitatively inherited traits controlled by numerous genes. The use of recurrent selection in self-pollinating crops depends on the ease of pollination, the frequency of successful hybrids from each pollination, and the number of hybrid offspring from each successful cross.
Each breeding program should include a periodic, objective evaluation of the efficiency of the breeding procedure. Evaluation criteria vary depending on the goal and objectives, but should include gain from selection per year based on comparisons to an appropriate standard, overall value of the advanced breeding lines, and number of successful cultivars produced per unit of input (e.g., per year, per dollar expended, etc.).
Promising advanced breeding lines are thoroughly tested and compared to appropriate standards in environments representative of the commercial target area(s) for three or more years. The best lines are candidates for new commercial cultivars; those still deficient in a few traits may be used as parents to produce new populations for further selection.
These processes, which lead to the final step of marketing and distribution, usually take from eight to 12 years from the time the first cross is made. Therefore, development of new cultivars is a time-consuming process that requires precise forward planning, efficient use of resources, and a minimum of changes in direction.
A most difficult task is the identification of individuals that are genetically superior, because for most traits the true genotypic value is masked by other confounding plant traits or environmental factors. One method of identifying a superior plant is to observe its performance relative to other experimental plants and to a widely grown standard cultivar. If a single observation is inconclusive, replicated observations provide a better estimate of its genetic worth.
The goal of plant breeding is to develop new, unique and superior canola cultivars and hybrids. The breeder initially selects and crosses two or more parental lines, followed by repeated selfing, and selection, producing many new genetic combinations. The breeder can theoretically generate billions of different genetic combinations via crossing, selfing, and mutations. The breeder has no direct control at the cellular level. Therefore, two breeders will never develop the same line, or even very similar lines, having the same canola traits.
Each year, the plant breeder selects the germplasm to advance to the next generation. This germplasm is grown under unique and different geographical, climatic and soil conditions and further selections are then made, during and at the end of the growing season. The cultivars that are developed are unpredictable. This unpredictability is because the breeder's selection occurs in unique environments, with no control at the DNA level (using conventional breeding procedures), and with millions of different possible genetic combinations being generated. A breeder of ordinary skill in the art cannot predict the final resulting lines he develops, except possibly in a very gross and general fashion. The same breeder cannot produce the same cultivar twice by using the exact same original parents and the same selection techniques. This unpredictability results in the expenditure of large amounts of research monies to develop superior new canola cultivars.
The development of new canola cultivars requires the development and selection of canola varieties, the crossing of these varieties and selection of superior hybrid crosses. The hybrid seed is produced by manual crosses between selected male-fertile parents or by using male sterility systems. These hybrids are selected for certain single gene traits such as pod color, flower color, pubescence color or herbicide resistance which indicate that the seed is truly a hybrid. Additional data on parental lines, as well as the phenotype of the hybrid, influence the breeder's decision whether to continue with the specific hybrid cross.
Pedigree breeding and recurrent selection breeding methods are used to develop cultivars from breeding populations. Breeding programs combine desirable traits from two or more cultivars or various broad-based sources into breeding pools from which cultivars are developed by selfing and selection of desired phenotypes. The new cultivars are evaluated to determine which have commercial potential.
Pedigree breeding is used commonly for the improvement of self-pollinating crops. Two parents that possess favorable, complementary traits are crossed to produce an F1. An F2 population is produced by selling one or several F1's. Selection of the best individuals may begin in the F2 population; then, beginning in the F3, the best individuals in the best families are selected. Replicated testing of families can begin in the F4 generation to improve the effectiveness of selection for traits with low heritability. At an advanced stage of inbreeding (i.e., F6 and F7), the best lines or mixtures of phenotypically similar lines are tested for potential release as new cultivars.
Mass and recurrent selections can be used to improve populations of either self- or cross-pollinating crops. A genetically variable population of heterozygous individuals is either identified or created by intercrossing several different parents. The best plants are selected based on individual superiority, outstanding progeny, or excellent combining ability. The selected plants are intercrossed to produce a new population in which further cycles of selection are continued.
Backcross breeding has been used to transfer genes for a simply inherited, highly heritable trait into a desirable homozygous cultivar or inbred line which is the recurrent parent. The source of the trait to be transferred is called the donor parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent. After the initial cross, individuals possessing the phenotype of the donor parent are selected and repeatedly crossed (backcrossed) to the recurrent parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent.
The single-seed descent procedure in the strict sense refers to planting a segregating population, harvesting a sample of one seed per plant, and using the one-seed sample to plant the next generation. When the population has been advanced from the F2 to the desired level of inbreeding, the plants from which lines are derived will each trace to different F2 individuals. The number of plants in a population declines each generation due to failure of some seeds to germinate or some plants to produce at least one seed. As a result, not all of the F2 plants originally sampled in the population will be represented by a progeny when generation advance is completed.
In a multiple-seed procedure, canola breeders commonly harvest one or more pods from each plant in a population and thresh them together to form a bulk. Part of the bulk is used to plant the next generation and part is put in reserve. The procedure has been referred to as modified single-seed descent or the pod-bulk technique.
The multiple-seed procedure has been used to save labor at harvest. It is considerably faster to thresh pods with a machine than to remove one seed from each by hand for the single-seed procedure. The multiple-seed procedure also makes it possible to plant the same number of seeds of a population each generation of inbreeding. Enough seeds are harvested to make up for those plants that did not germinate or produce seed.
Descriptions of other breeding methods that are commonly used for different traits and crops can be found in one of several reference books (e.g., Allard, 1960; Simmonds, 1979; Sneep et al., 1979; Fehr, 1987).
Proper testing should detect any major faults and establish the level of superiority or improvement over current cultivars. In addition to showing superior performance, there must be a demand for a new cultivar that is compatible with industry standards or that creates a new market. The introduction of a new cultivar will incur additional costs to the seed producer, the grower, processor and consumer; for special advertising and marketing, altered seed and commercial production practices, and new product utilization. The testing preceding release of a new cultivar should take into consideration research and development costs as well as technical superiority of the final cultivar. For seed-propagated cultivars, it must be feasible to produce seed easily and economically.
One particular broad spectrum herbicide that has been the subject of much investigation is N-phosphonomethyl-glycine, also known as glyphosate. Glyphosate has been used extensively by farmers worldwide for controlling weeds prior to crop planting, for example, in no-till farming. In addition, glyphosate is an efficient means to control weeds and volunteer plants between production cycles or crop rotations. Glyphosate does not carry-over in soils after use, and it is widely considered to be one of the most environmentally safe and broadly effective of chemical herbicides available for use in agriculture.
Glyphosate kills plants by inhibiting the shikimic acid pathway. This pathway leads to the biosynthesis of aromatic compounds, including amino acids, vitamins and plant hormones. Glyphosate blocks the conversion of phosphoenolpyruvic acid (PEP) and 3-phosphoshilkimic acid to 5-enolpyruvyl-3-phosphoshikimic acid by binding to and inhibiting activity of the enzyme 3-enolpyruvylshikimate-3-phosphate synthase, commonly referred to as EPSP synthase, or EPSPS.
Unfortunately, no crop plants are known that are naturally tolerant to glyphosate and, therefore, the utility of this herbicide for weed control in cultivated crops has been limited. One method to produce glyphosate tolerant crop plants is to introduce a gene encoding a heterologous glyphosate tolerant form of an EPSPS gene into the crop plant using the techniques of genetic engineering. Using chemical mutagenesis, glyphosate tolerant forms of EPSPS were produced in bacteria and the heterologous genes were introduced into plants to produce glyphosate tolerant plants (see, e.g., Comai et al., Science 221:370-71 (1983)). The heterologous EPSPS genes are usually overexpressed in the crop plants to obtain the desired level of tolerance. Thus, for a number of reasons it is desirable to produce a non-GMO sunflower that is resistant to glyphosate.
Canola, Brassica napus oleifera annua, is an important and valuable field crop. Thus, a continuing goal of plant breeders is to develop stable, high yielding canola cultivars that are agronomically sound. The reasons for this goal are obviously to maximize the amount of grain produced on the land used and to supply food for both animals and humans. To accomplish this goal, the canola breeder must select and develop canola plants that have the traits that result in superior cultivars.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification.